Recently, in various industrial facilities and environmental foundations, malodors and waste gas polluted with volatile organic chemicals (VOC) are discharged to air a lot and cause air pollution. VOC is mainly composed of organic acid, aldehydes, ketones, aromatic compounds and the like and malodor inducers are commonly consisted in sulfide system substances such as hydrogen sulfide and methylmercapthane and nitrogen system substances such as ammonia and amines. Besides, waste gas has a wide spectrum in its state, depending upon the outlet source of waste gas such as an industrial factory.
Presently, various physical, chemical and biological methods have been tried to remove VOC and malodors included in air. For example, the cooling concentration method, the catalyst-type combustion method, the physical adsorption method, the cleaning method and the like have been utilized. Although the physical and chemical method among these removes polluted gas efficiently, it costs too much price to be operated for facilities, material, chemicals and the like. Furthermore, it is not economical to reduce the concentration of waste gas and to reach the outlet limit for the permission and also generates secondary contaminants such as SOx, CO, NOx. Therefore, the cleaning techniques have been developed continuously to be more favorable to environment, to have a higher efficiency and to reduce the price. Consequently, the biofiltration method in which VOC and malodors are converted to carbon dioxide and other material without or with less malodor is on the rise.
Compared with other methods for reducing malodors and VOC, the biofiltration technology is so outstanding that it requires less investment and cheap operation price, consumes less energy, produces chemicals with a low concentration and uses less fuel, as well as that it rarely generates secondary contaminants.
Unfortunately, there are a lot of problems in the conventional apparatus for removing odor and VOC by using biofilters. Concretely, (i) as the operation time using the biofilters increases, the empty space of carriers might be blocked by the microorganismic layer formed in accordance with the bacterial growth. Therefore, (ii) the removal rate is good in the initial stage, but air pores within carriers are clogged gradually as microorganisms proliferate much, which causes a biased flow of air, reduces the capacity of biofilters drastically and consumes electric power a lot since the pressure is lost highly. In addition, (iii) it is necessary to stir, wash and change carriers periodically in order to delete the microorganismic layer formed from the cell growth and (iv) the apparatus is large in the size and needs a wide space to be installed since it has a long retention period to treat polluted gas for about 30 seconds˜ 3 minutes. Hence, the malodors and VOC are not managed efficiently and stably in practice. Especially, the problems which are provoked by use of the existed biofilters become still more serious, when the waste gas with the high content of organic compounds is treated.
Besides, there is another problem in the conventional apparatus for removing polluted gas by using the biofilters derived from the conventional technique. In detail, it has a disadvantage to provide nutrients for the bacterial growth. Since in the conventional process by using biofilters, the nutrients are added in a liquid state, it is necessary not to be freezed in winter season, to regulate temperatures for preventing the release of nutrients, to furnish a stirrer for preventing the precipitation, not to be contaminated by bacteria when it is left for a long time and the like.
Necessarily, new methods for eliminating polluted gas should be established to settle disadvantages demonstrated above, even in the prolonged operation.